title: Focal autoimmune pancreatitis: radiological characteristics help to distinguish from pancreatic cancer.
abstract: OBJECTIVE
  To identify the radiological characteristics of focal autoimmune pancreatitis (f-AIP) useful for differentiation from pancreatic cancer (PC).
  
  
  METHODS
  Magnetic resonance imaging (MRI) and triple-phase computed tomography (CT) scans of 79 patients (19 with f-AIP, 30 with PC, and 30 with a normal pancreas) were evaluated retrospectively. A radiologist measured the CT attenuation of the pancreatic parenchyma, the f-AIP and PC lesions in triple phases. The mean CT attenuation values of the f-AIP lesions were compared with those of PC, and the mean CT attenuation values of pancreatic parenchyma in the three groups were compared. The diagnostic performance of CT attenuation changes from arterial phase to hepatic phase in the differentiation between f-AIP and PC was evaluated using receiver operating characteristic (ROC) curve analysis. We also investigated the incidence of previously reported radiological findings for differentiation between f-AIP and PC.
  
  
  RESULTS
  The mean CT attenuation values of f-AIP lesions in enhanced phases were significantly higher than those of PC (arterial phase: 60 ± 7 vs 48 ± 10, P < 0.05; pancreatic phase: 85 ± 6 vs 63 ± 15, P < 0.05; hepatic phase: 95 ± 7 vs 63 ± 13, P < 0.05). The mean CT attenuation values of f-AIP lesions were significantly lower those of uninvolved pancreas and normal pancreas in the arterial and pancreatic phase of CT (P < 0.001, P < 0.001), with no significant difference at the hepatic phase or unenhanced scanning (P = 0.4, P = 0.1). When the attenuation value increase was equal or more than 28 HU this was considered diagnostic for f-AIP, and a sensitivity of 87.5%, specificity of 100% and an area under the ROC curve of 0.974 (95%CI: 0.928-1.021) were achieved. Five findings were more frequently observed in f-AIP patients: (1) sausage-shaped enlargement; (2) delayed homogeneous enhancement; (3) hypoattenuating capsule-like rim; (4) irregular narrowing of the main pancreatic duct (MPD) and/or stricture of the common bile duct (CBD); and (5) MPD upstream dilation ≤ 5 mm.
  
  
  CONCLUSIONS
  Analysis of a combination of CT and MRI findings could improve the diagnostic accuracy of differentiating f-AIP from PC.
authors.affiliation: Department of Radiology, Changhai Hospital, the Second Military Medical University, Shanghai 200433, China.
authors.forename: Gao-Feng
authors.initials: GF
authors.lastname: Sun
authors.forename: Chang-Jing
authors.initials: CJ
authors.lastname: Zuo
authors.forename: Cheng-Wei
authors.initials: CW
authors.lastname: Shao
authors.forename: Jian-Hua
authors.initials: JH
authors.lastname: Wang
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000368:Aged; D019540:Area Under Curve; D001327:Autoimmune Diseases / Q000000981:diagnostic imaging* / Q000276:immunology; D049448:Cholangiopancreatography, Magnetic Resonance; D003287:Contrast Media; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging*; D010195:Pancreatitis / Q000000981:diagnostic imaging* / Q000276:immunology; D011237:Predictive Value of Tests; D012372:ROC Curve; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed
chemical_list: D003287:Contrast Media
keywords: Computer tomography; Focal autoimmune pancreatitis; Magnetic resonance cholangiopancreatography; Magnetic resonance imaging; Pancreatic cancer